When building or upgrading a high-performance Ford Duratec engine, one of the most critical yet often overlooked components is the valvetrain—specifically, the valve springs. The STK Single Valve Spring Kit for Ford ST150/170 is designed to handle the increased demands of modified engines, ensuring reliability, stability, and performance at high RPM.
Product Overview
The STK Performance single valve spring kit is a high-performance upgrade engineered specifically for the Ford ST150 and ST170 platforms. Built using premium materials and motorsport-focused design, this kit is tailored for engines running higher rev limits, aggressive camshafts, or forced induction setups.
At its core, the kit replaces the factory valve springs with stronger, more durable components that maintain precise valve control under extreme conditions.
What’s Included:
- 16 × Single valve springs
- 16 × Chromoly retainers
Key Specifications:
- Seat pressure: 85 lbs @ 34mm
- Open pressure: 175 lbs at full lift
- RPM capability: Up to 8500 RPM
- Lift capacity: Up to 12mm cam lift
Why Valve Springs Matter
Valve springs are responsible for controlling the opening and closing of engine valves. In a standard engine, factory springs are designed for moderate RPM and mild cam profiles. But once you start modifying the engine—adding cams, boost, or increasing rev limits—the stock springs quickly become a weak point.
Upgraded valve springs like this STK kit are essential because they:
- Prevent valve float (when valves fail to close properly at high RPM)
- Maintain accurate valve timing
- Improve engine reliability under load
- Ensure consistent sealing and combustion
Without proper valve spring support, even a well-built engine can suffer from power loss—or worse, catastrophic failure.
Performance Benefits
1. Eliminates Valve Float
At high RPM, factory springs can’t keep up with the rapid movement of the valvetrain. This kit provides stronger spring pressure to keep everything under control, even at extreme revs.
2. High-RPM Stability
Rated up to 8500 RPM, these springs are ideal for track builds, spirited driving, and high-performance street setups.
3. Supports Aggressive Camshafts
If you’re running high-lift or long-duration cams, upgraded springs are non-negotiable. This kit is designed to handle up to 12mm lift, making it perfect for performance camshaft setups.
4. Prevents Coil Bind
The springs are engineered to resist coil bind (when the spring compresses fully and fails), even under extreme conditions.
5. Improved Engine Efficiency
Better valve control leads to:
- More consistent combustion
- Improved power delivery
- Increased overall engine efficiency
Materials & Engineering
One of the standout features of this kit is its material quality.
- Chrome Silicon Steel (CrSi):
Known for exceptional strength, heat resistance, and fatigue life—perfect for high-performance engines. - Shot Peened & Heat Treated:
Enhances durability and prevents premature failure under stress. - 4130 Chromoly Retainers:
Lightweight yet extremely strong, reducing valvetrain mass and improving response.
This combination ensures long-term reliability, even in demanding motorsport environments.
Ideal Applications
This valve spring kit is best suited for:
- Naturally aspirated builds with upgraded camshafts
- Turbocharged or supercharged setups
- Track cars and race builds
- High-performance daily drivers
The Ford ST150 (Duratec 2.0) and ST170 (Zetec-based performance variant) are both known for being rev-happy platforms, making them perfect candidates for this type of upgrade.
Installation Notes
This is not a basic bolt-on part—you’re dealing with the engine’s internal components. Proper installation is critical.
- Professional installation is strongly recommended
- Always verify:
- Installed spring height
- Coil bind clearance
- Piston-to-valve clearance
- Use proper break-in procedures and oil
Incorrect setup can lead to serious engine damage.
Single vs Dual Valve Springs
This kit uses a single spring design, which offers:
Advantages:
- Lower weight (less valvetrain inertia)
- Reduced friction
- Simpler setup
Trade-offs:
- Slightly less harmonic damping than dual springs (but still highly capable for most builds)
For the majority of performance street and track applications, a well-designed single spring setup like this is more than sufficient.
Final Verdict
The STK Single Valve Spring Kit for Ford ST150/170 is a must-have upgrade for anyone pushing their Duratec or ST170 engine beyond factory limits.
It delivers:
- Reliable high-RPM performance
- Strong, durable materials
- Compatibility with aggressive builds
- Proven motorsport capability
If you’re upgrading cams, increasing rev limits, or building a serious performance engine, this kit isn’t optional—it’s essential.